Make sure you're drinking plenty of water if exercising. Daft as it sounds, exercising has been known to slow weight loss - have you checked to see if you've lost inches instead of pounds?
Sometimes exercising more than usual can slow down your weight-loss for a couple of weeks.
I stayed the same last week and only 1lb off my 2st award. This week i've been doing exercise (i'm usually allergic lol) and have really enjoyed it and expecting another STS but i'm going to be quite gutted if i don't lose for another week